1. Field of the Invention
The present invention relates to a liquid jet head and a liquid jet apparatus for ejecting liquid from a nozzle to record graphics and characters on a recording medium, or to form a functional thin film thereon.
2. Description of the Related Art
In recent years, there has been used an ink-let type liquid jet head for ejecting ink droplets on recording paper or the like to record characters or graphics thereon, or for ejecting a liquid material on a surface of an element substrate to form a functional thin film thereon. In such a liquid jet head, ink or a liquid material, is supplied from a liquid tank via a supply tube to the liquid jet head, and ink or a liquid material filled into a channel is ejected from a nozzle which communicates with the channel. When ink is ejected, the liquid jet head or a recording medium on which a pattern of jetted liquid is to be recorded is moved to record characters or graphics, or to form a functional thin film in a predetermined shape.
Japanese Patent Application Laid-open No. 2011-93200 describes a liquid jet head 100 of this type. FIG. 7 is a perspective view of the liquid jet head illustrated in FIG. 5(b) of Japanese Patent Application Laid-open No. 2011-93200. The liquid jet head 100 has a laminated structure of a nozzle plate 101, a piezoelectric plate 102, a cover plate 103, and a flow path member 104. The piezoelectric plate 102 includes a channel row in which a plurality of channels are arrayed. The cover plate 103 closes opening portions of the plurality of channels, and includes a liquid supply chamber 106 for supplying liquid to the respective channels, and a liquid discharge chamber 107 for discharging the liquid from the respective channels. The flow path member 104 includes a supply joint 105a through which liquid from an external liquid tank (not shown) flows in, and a discharge joint 105b through which the liquid returns to the liquid tank. The nozzle plate 101 includes nozzles 112 communicated with respective ejection channels 110a (see FIGS. 8A to 8C).
The liquid supplied from the liquid tank (not shown) flows into the liquid supply chamber 106 via the supply joint 105a, and is filled into the channel row formed of the plurality of channels. Then, the liquid flows out from the channel row toward the liquid discharge chamber 107, and returns to the liquid tank via the discharge joint 105b. Therefore, the liquid constantly circulates during driving. An air bubble and dust mixed into the liquid circulate and return to the liquid tank together with the liquid. Therefore, occurrence of nozzle clogging is reduced. As a result, liquid replacement and maintenance such as cleaning of the liquid jet head 100 are facilitated, the amount of liquid to be consumed during cleaning is reduced, and the consumption amount of the recording medium is reduced as well. Therefore, there is such an advantage that increase of running cost can be suppressed. Japanese Patent No. 4263742 also describes a liquid circulating type ink jet head.
FIG. 8A is a schematic plan view of the cover plate 103 of the liquid jet head 100, from which the flow path member 104 is removed. FIG. 8B is a schematic sectional view of the liquid jet head 100 taken along the line A-A of FIG. 8A. FIG. 8C is a schematic sectional view of the liquid jet head 100 taken along the line B-B of FIG. 8A.
As illustrated in a partial enlarged view of FIG. 8C, the piezoelectric plate 102 includes the ejection channels 110a and dummy channels 110b which are alternately arrayed. The cover plate 103 includes a plurality of slits 109 formed in the liquid supply chamber 106 and the liquid discharge chamber 107 on the piezoelectric plate 102 side. The ejection channel 110a are communicated with the liquid supply chamber 106 via the slits 109, and the dummy channels 110b are closed by the cover plate 103.
The supply joint 105a of the flow path member 104 is positioned at substantially the longitudinal center of the liquid supply chamber 106, and the discharge joint 105b or the flow path member 104 is positioned at substantially the longitudinal center of the liquid discharge chamber 107. The liquid flows in via the supply joint 105a to fill the liquid supply chamber 106 up to both end portions thereof. Then, the liquid flows through the respective ejection channels 110a to be discharged to the liquid discharge chamber 107, and then returns to the liquid tank (not shown) via the discharge joint 105b. 
However, in the liquid jet head 100 of this type, as illustrated in FIG. 8C, an air bubble 111 mixed into the liquid may adhere to end portions of the slits 109 to remain inside the liquid supply chamber 106. When the air bubble 111 adheres to the opening portions of the slits 109, the liquid cannot be supplied to the ejection channels 110a, and liquid droplets cannot be ejected at a constant condition. Even when the liquid is pumped from the supply joint 105a side in order to remove the air bubble 111, because the flow path resistance of the ejection channel 110a is large, the air bubble 111 may not be discharged toward the liquid discharge chamber 107 via the ejection channels 110a. It is desired to obtain a liquid jet head 100 capable of, even when the air bubble 111 is mixed into the liquid, removing the air bubble 111 to the outside.